I always give it a go but give up after ten minutes of going trough what really mostly is garbage. The endless row of cheap compilations and musicians you'd wish they never made a record, all unorganized an put down on the floor so you're doing you're daily squat exercises without getting a reward for it. I never picked anything up from it. As I also have limited storing space I try not to buy any 'let's give that one a try' records but only stuff that's on my wishlist. The chance of them being in one of those bins is nihil.
But I'm always tempted when I see them. Thursday is a national holiday here: Kings day. Lot's of flea markets with hundreds of bins filled with these guys: